Field of the Invention
This invention is related to processors and, more particularly, to resetting processors and vectoring after reset.
Description of the Related Art
Processors are generally used in digital systems of various types to control other hardware in the system and to execute software to provide desired functionality for the user. When the digital system is first powered on, typically the processor is reset via assertion of a reset signal to the processor. The reset causes the processor to initialize to a known state from which execution can begin. The processor can then be released from reset. In response to the release from reset, the processor can begin instruction execution beginning at a known address. The known address is referred to as the reset vector address, or more briefly the reset vector. Instructions stored at the reset vector address can be executed to initialize the processor resources, various other hardware resources in the system, etc. One or more instructions that are executable by a processor to perform a task or tasks are collectively referred to as code, or a program, in this description.
Originally, the reset vector address was hardwired in the processors. While the hardwiring of the reset vector address provides predictability and simplicity, the hardwiring is inflexible. Different systems may be more amendable to having the reset vector at different addresses. To address this, some processors are configured to receive a reset vector address on an input to the processor. The input is hardwired in the system to be the reset vector address that is desired by that particular system. While the processor is more flexible for use in different systems, a given system is still required to have a hardwired reset vector address.